Wireless sensors spend most of the time in an ultra-low-power sleep state with their radios off to conserve energy. This presents a problem for remotely waking up and synchronizing to these nodes. Wake-up radios (WRX) are a viable solution, but only if their active power is below the sleep power of the node, otherwise the WRX power dominates and dictates the lifetime of the node. With digital sleep power being reported in the nW range, this presents a significant challenge to WRX design. A simple method for reducing the power of a WRX is to reduce sensitivity, which is tolerable for short-range communication and when the primary goal is a lifetime of multiple years. For example, with a receiver sensitivity of −40 dBm, 6 m communication at 400 MHz is possible with only 0 dBm transmit power. This is suitable for a broad range of medical and internet of things applications.
Most published WRXs use energy detection architectures to keep power low; however, any signal at the proper frequency can trigger a false wake-up of these radios, and false wake-ups result in significant amounts of wasted energy on the node. In order to prevent this, a WRX must have enough local processing to differentiate a wake-up event from interference without use of the node's main processor. This disclosure presents a 116 nW wake-up receiver complete with crystal reference, interference compensation, and all the necessary baseband processing, such that a selectable 31-bit code is required to toggle a wake-up signal. The front-end operates over a broad frequency range, tuned by an off-chip band-select filter and matching network, and is demonstrated in the 403 MHz MICS band, and the 915 MHz and 2.4 GHz ISM bands. Additionally, the baseband processor implements automatic threshold feedback to detect the presence of interferers and dynamically change the receiver's sensitivity, mitigating the jamming problem inherent to previous energy-detection WRXs.
This section provides background information related to the present disclosure which is not necessarily prior art.
This section provides background information related to the present disclosure which is not necessarily prior art.